The present invention relates to a method of manufacturing adsorbents. More particularly, it relates to a method of manufacturing carbonaceous adsorbents impregnated with elementary sulfur.
For removing harmful or even poisonous material, such as quick silver, from waste gases, for example from surrounding air in laboratories operating with quick silver, it is known to use as a rule activated coal impregnated with materials which bind quick silver. In particular, activated coal impregnated with elementary iodine is used for this purpose. Such activated coal is obtained by impregnating of it with sulfuric acid and potassium iodide. Moreover, it is known that activated coal impregnated with elementary sulfur is especially suitable for removing quick silver vapors from air or other gases, as disclosed for example in "Chemical Engineering Progress" Vol. 70 (1974), page 45.
As a rule, the manufacture of impregnated activated coal is carried out by a soaking process in which the desired content of the material to be provided is adjusted by concentration of the soaking solution and the number of the soaking steps. It is possible in this manner to provide in general not more than 10-12 weight % of the desired material. Metallic materials can be put in immediately prior to or during the activating treatment of the coal.
Forcing-in of elementary sulfur during the activated coal manufacture is, however, not possible since the sulfur evaporates at the temperatures of the activation of 800.degree.-900.degree. C., or when it has not been evaporated it is converted during the water vapor activation into hydrogen sulfide.
With the utilization of the soaking process for charging with elementary sulfur, the sulfur must be dissolved in a suitable solvent, soaked with the activated coal, and subsequently again vaporized. There are suitable solvents for this purpose, but this is connected in all soaking processes with serious disadvantages.
Elementary sulfur dissolves for example in an ammonium polysulfide solution or in an organic solvent, such as carbon disulfide, benzene, toluene and alcohols. A soaking with a polysulfide solution is excluded on the grounds of environmental protection, since considerable waste air and waste water problems occur. In the event of soaking with sulfur dissolved in organic solvents, the solvent must be again vaporized after the soaking. Since activated coal adsorbs in addition to the sulfur simultaneously 50-100 weight % of the solvent, considerable quantities of heat are required for desorption and removal of the solvent. Moreover, for putting in of 20-30 weight % of sulfur, at least 2-3 soaking steps are required.
A further possibility of putting in of sulfur to an activated coal is provided by a catalytic H.sub.2 S oxidation of H.sub.2 S-containing gases in a reactor accommodating an activated coal. Such a method is, however, very expensive and does not produce uniform sulfur loading on the activated coal. The same disadvantages are encountered when sulfur is separated from a sulfur-containing gas stream flowing through activated coal, directly by adsorption. As required by the low vapor pressure of the sulfur (at 200.degree. C. only 0.02 kg S/m.sup.3 gas), such a method can be carried out at temperatures of above 200.degree. C.